The subject matter disclosed herein relates generally to power conversion systems and more specifically to use of energy storage in conjunction with power conversion systems of renewable energy sources.
In conventional control approaches for renewable energy sources with dual stage power conversion, a source side converter is coupled in parallel by DC (direct current) link to a grid side converter. In a wind turbine embodiment, for example, a source side controller uses wind turbine generator torque regulation to control the source side converter, and a grid side controller uses DC voltage regulation to control the grid side converter. Other examples of renewable energy sources include solar and marine hydrokinetic energy sources.
A goal of the source side controller when providing power from a renewable energy source is to transmit as much of the source power to the grid as possible, whereas a goal of the grid side converter is to satisfy grid interconnection requirements that affect power output such as ramp rate limits, governor droop control, curtailment, and fault ride through. These different control objectives for source and grid side control sometimes result in a power imbalance on the DC link that causes charging or discharging of the DC link capacitor resulting in undesirable voltage fluctuations.